N-15 and C-13 Nuclear-Magnetic-Resonance of Deoxydinucleotide Monophosphates .2. Protonation of the Homo Dimers Deoxycytidylyl-(3',5')-Deoxycytidine, Thymidylyl-(3',5')-Thymidine, and Deoxyadenylyl-(3',5')-Deoxyadenosine in Dimethyl-Sulfoxide

The preferential protonation sites of homo dimers d(cpC), d(TpT), and d(ApA) were established by nitrogen-15 and carbon-13 NMR in DMSO, in the presence of varying amounts of trifluoroacetic acid. The 15N NMR data show that in the d(CpC) the capability of the two N3 nitrogens to accept the proton is slightly different. In d(TpT) and d(ApA) the protonation of the phosphate group leads to significant variations of the chemical shift of the carbons adjacent to the phosphorus.